The invention relates to an optoelectronic code reader and to a method for the reading in of codes which move relative to the code reader inside a reading zone, with the reading zone being scanned at least along a scan direction.
Such a reading in of codes takes place with a barcode scanner, for example, in that a laser beam is periodically guided over the reading zone along the scan direction by means of a rotating polygon mirror, with the reflected light being supplied to a light receiver. Depending on whether the laser beam is reflected at a light or a dark surface, a light amount of a different strength is incident on the receiver. The corresponding output signals of the receiver are evaluated with respect to the presence, and where applicable to the content, of a barcode by means of an evaluation device.
Optical codes can also be read in, for example, by means of a line scan camera which is able to scan linear image information corresponding to the scan direction simultaneously by means of a plurality of light receiving elements arranged in a line in order to subsequently evaluate these for the presence of a code.
The scanning of the reading zone at least along the scan direction is necessary with such code readers since, with the usual codes, the information to be read in along an information arrangement device is encoded. For instance, a barcode consists, for example, of light and dark bars which are arranged next to one another along the information arrangement direction. Only when the scan direction agrees with the information arrangement direction or adopts a certain critical scanning angle can the code be read in correctly.
It is a common feature of this kind of code readers that they have a limited focusing range, that is, a limited depth of field. This can result in problems if a plurality of codes should be read in successively which are arranged at objects—for example mail packages—of a different height and thus adopt different distances to the code reader. In this case, all the codes can only be read in correctly if a matching of the focal position of the code reader is carried out between the scanning of the different codes.
However, this remedy is also problematic, and indeed in particular when the different codes are moved through the reading zone of the code reader along a conveying direction and should be scanned along a scan direction which extends perpendicular or diagonally to the conveying direction. The situation can occur in this case that two codes are arranged along the scan direction in the reading zone of the code reader which adopt a different distance to the code reader.
If the focal position is changed in this situation during the scanning along a scan direction, in order to correctly read in both codes, the movement of the code along the conveying direction can at best take place at a very reduced speed at times. The changing of the focal position namely requires a certain length of time so that scanning along the scan direction requires a corresponding minimum time. If, however, the codes are moved too fast in the conveying direction during scanning, the code to be read in last has possibly already left the scan line before the total scanning process along the scan line has been completed.